10 NATURAL INHERITANCE. [chap. 



tion under separate heads, but as different effects of the 

 same underlying causes. 



The origin of these and other prominent processes 

 in heredity is best explained by illustrations. That 

 which will be used was suggested by those miniature 

 gardens, self-made and self-sown, that may be seen 

 in crevices or other receptacles for drifted earth, on 

 the otherwise bare faces of quarries and cliffs. I have 

 frequently studied them through an opera glass, and 

 have occasionally clambered up to compare more closely 

 their respective vegetations. Let us then suppose the 

 aspect of the vegetation, not of one of these detached 

 little gardens, but of a particular island of substantial 

 size, to represent the features, bodily and mental, of 

 some particular parent. Imagine two such islands 

 floated far away to a desolate sea, and anchored 

 near together, to represent the two parents. Next 

 imagine a number of islets, each constructed of earth 

 that was wholly destitute of seeds, to be reared near to 

 them. Seeds from both of the islands will gradually 

 make their way to the islets through the agency of 

 winds, currents, and birds. Vegetation will spring up, 

 and when the islets are covered with it, their several 

 aspects will represent the features of the several children. 

 It is almost impossible that the seeds could ever be 

 distributed equally among the islets, and there must be 

 slight differences between them in exposure and other 

 conditions, corresponding to differences in pre-natal 

 circumstances. All of these would have some influence 

 upon the vegetation ; hence there would be a corre- 



